Plant Kingdom Class 11 Biology NCERT Solutions

Step-by-step solution

1. 1The basis is a combination of pigment, flagellation and stored food, together with the cell wall and the plant body, and the NCERT scheme classifies algae on three main grounds: morphology, physiology and biochemistry.
2. 2On morphological grounds algae are placed by cell structure, the body organisation, the pigments present, the stored food, the cell wall composition, the form of growth, the flagella and their arrangement in the cell, and the habitat and geographical distribution. So a unicellular filamentous alga with a pear-shaped body and two flagella goes to Chlamydomonas, while a multicellular colonial one with a coenobium goes elsewhere.
3. 3On physiological grounds the classification rests on the photosynthetic pigments, the stored food, the cell wall constituents, the life cycle phases, and the flagellar structure and its place of insertion. The pigments are the most decisive of these, because they follow photosynthesis itself: chlorophyll a with chlorophyll b and carotene means a green alga, chlorophyll a with chlorophyll d means a red alga, chlorophyll a and c with fucoxanthin means a brown alga, and chlorophyll a with carotene and no chlorophyll b means a diatom.
4. 4On biochemical grounds the classification uses the stored food, the cell wall chemistry, the pigments and the nucleic acid composition, so it is the most reliable of the three, since the chemical components are the least variable characters.
5. 5The exam answer to give is therefore that algae are classified on the basis of pigment, stored food, cell wall composition, flagellar structure and life cycle pattern, and that of these the photosynthetic pigment is the primary criterion, since the pigments and the food they store are the most reliable characters.

Step-by-step solution

1. 1Reduction division is meiosis, and it takes place in the spore mother cells. The rule is that it happens in the sporophyte generation, in the sporangium or the nucellus, and the time depends on where and when spores are formed in the life cycle. So the answer for each group is the same process in a different place.
2. 2In a liverwort, which is haplodiplontic, the sporophyte is the small capsule on a seta, and the reduction division takes place in the capsule, that is in the sporophyte, and it produces haploid spores. The dominant plant is the gametophyte, so the sporophyte is the dependent generation.
3. 3In a moss, also haplodiplontic, the sporophyte is the capsule with its foot and seta, and the reduction division again takes place in the capsule of the sporophyte, producing haploid spores, and the dominant plant is the gametophyte.
4. 4In a fern, also haplodiplontic but with both generations independent, the sporophyte is the familiar plant, and the reduction division takes place in the sporangia, which are borne in sori on the underside of the fronds, so it is again in the sporophyte.
5. 5In a gymnosperm the sporophyte is the plant, and the reduction division takes place in the microsporangium and the megasporangium, that is in the pollen sac and in the nucellus of the ovule. The microsporangium gives the four-celled pollen, and the megasporangium gives the single megaspore, so the male gametophyte here is the pollen and the female is retained in the ovule.
6. 6In an angiosperm the sporophyte is the plant, and the reduction division takes place in the microsporangium, the pollen sac of the anther, giving the four-celled pollen grain, and in the megaspore mother cell of the nucellus of the ovule, which undergoes meiosis to give the single functional megaspore and the other three degenerating.
7. 7The unifying statement to close with is that reduction division always occurs in the sporophyte, always in a cell derived from the sporophyte, and always yields haploid spores, and the difference between the groups is only in the organ of the sporophyte in which it occurs and in how soon in the life cycle it happens.

Step-by-step solution

1. 1The three groups are the bryophytes, the pteridophytes and the gymnosperms, and together they are called the archegoniates or, more precisely, the Embryophyta, since the archegonium is the structure in which the female gamete is formed and it is the feature that unites them.
2. 2Take the fern, a pteridophyte, for the life cycle. The plant that everyone recognises, the fern plant, is the sporophyte, and it is diploid, so it is the dominant generation.
3. 3The sporangia are borne in clusters called sori on the underside of the fronds, and inside the sporangium are the spore mother cells. These undergo meiosis, the reduction division, to produce haploid spores, and this is the only place in the fern life cycle where reduction division occurs.
4. 4The spores fall onto moist soil and germinate into a small, green, free-living, photosynthetic, heart-shaped thalloid gametophyte called a prothallus. It is haploid, so the prothallus is the gametophyte, and in a fern it is independent of the sporophyte, which is a feature that distinguishes ferns from the bryophytes.
5. 5The prothallus bears the sex organs, the antheridia and the archegonia, at its ventral surface near the notch, and each is jacketed by a sterile layer. The antheridia produce the male gametes, which are biflagellate, motile, water-dependent antherozoids, and the archegonia produce the female gamete, the egg.
6. 6Water is essential here, because the antherozoids are flagellated and have to swim from the antheridium to the archegonium, so fertilisation needs a film of water and is an oogamous fertilisation. The zygote is diploid and it is retained within the archegonium.
7. 7The zygote develops into an embryo and then into a sporophyte, and this young sporophyte is initially dependent on the prothallus, which supplies it until the first roots, leaves and fronds grow and it becomes independent. The cycle is therefore haplodiplontic, since both the sporophyte and the gametophyte are multicellular and free-living. The same life cycle with slight variations describes the bryophytes and the gymnosperms, and the gymnosperm is the only archegoniate in which the female gametophyte is retained within the ovule and never leaves it.

Step-by-step solution

1. 1This is a ploidy question, and the answer is found by asking one thing in each case: is the structure part of the gametophyte, part of the sporophyte, or the product of a fusion? Gametophyte structures are haploid, sporophyte structures are diploid, and a zygote is diploid because it is a fusion product.
2. 2Protonemal cell of a moss: haploid or n. The protonema is the first phase of the gametophyte, arising from the germination of a haploid spore, so it is n.
3. 3Primary endosperm nucleus in a dicot: triploid or 3n. In an angiosperm the endosperm is formed by triple fusion, in which one male gamete fuses with two polar nuclei, so 1n plus 2n gives 3n. This is the one diploid-independent structure in the list, and it is the reason a dicot seed needs endosperm at all.
4. 4Leaf cell of a moss: haploid or n. The leafy plant is the gametophyte, since the sporophyte of a moss is the dependent capsule with seta.
5. 5Prothallus cell of a fern: haploid or n. The prothallus is the fern gametophyte, and both generations are independent in a fern.
6. 6Gemma cell in Marchantia: haploid or n. Marchantia is a liverwort, so the thallus that bears the gemma cup is the gametophyte, and a gemma is a clone of it, so n.
7. 7Meristem cell of a monocot: diploid or 2n. Meristematic tissue is part of the sporophyte body, so every meristem cell of a flowering plant is 2n.
8. 8Ovum of a liverwort: haploid or n. The egg is a gamete, formed by mitosis in the gametophyte, so it is n.
9. 9Zygote of a fern: diploid or 2n. The zygote is formed by fusion of two haploid gametes and is therefore the first diploid cell of the cycle.
10. 10Note on the text: the NCERT book prints the third item of this question as 'a ferm', which is a typographical error for 'a fern'; the prothallus is the fern gametophyte, so the prothallus cell is n.

Step-by-step solution

1. 1Split the answer in two, since algae and gymnosperms contribute in completely unrelated ways. The algae matter mainly to industry, to food and to agriculture, and the gymnosperms mainly to timber, to fuel and to industry.
2. 2The economic importance of algae begins with food and fodder. Chlorella and Spirulina are used as food supplements because they are rich in proteins, vitamins and minerals, and Spirulina is also used as a single-cell protein source. Fish and poultry feed, and the agar-agar used in microbiology and in making jams, both come from algae.
3. 3The second group of uses is industrial and agricultural. Algae give us iodine from the red and brown algae, algin from the brown algae for making alginate, and carrageenan as a thickener. Microalgae are grown in sewage treatment to clear the water, and the biofertilisers from Spirulina and Chlorella enrich the soil, which is why the chapter calls them the photosynthetic Henry Ford of the future, since they can produce food, oil and fuel.
4. 4The economic importance of gymnosperms starts with wood. The wood of Pinus, Deodar, Cedrus and other gymnosperms is used for construction and furniture, and it is a preferred timber for railway sleepers and for the poles of electric lines, because the wood is hard, resinous and resistant to decay.
5. 5The second use is as fuel and as a source of industry. The wood and the resin of Pinus give turpentine, rosin, benzoin, terpene and the resins, and Pinus is also the source of turpentine oil and of the resin used in making varnishes. Cycas seeds yield a flour used as food, and Ephedra, a gymnosperm, yields ephedrine, which is used in treating asthma and hay fever.
6. 6Two further points to add for completeness: the gymnosperms are the source of the resin and of wood for sawing and papermaking, and some of them such as Cedrus deodara are grown for afforestation and for ornament, while Cycas and Ephedra are standard examples in the examination.

Step-by-step solution

1. 1The premise is only half true, and the answer begins by correcting it carefully: both bear seeds, but the seed is borne in a different position, and that single difference is enough to separate the two groups. The other differences then follow from it.
2. 2The decisive character is the enclosure of the ovule. In a gymnosperm the ovule and the seed are naked and exposed, borne directly on the megasporophyll, and they are not enclosed within any fruit. The name gymnosperm means naked seed. In an angiosperm the ovule is enclosed within an ovary, and the ovary later ripens into a fruit, so the seed is enclosed within a fruit. The name angiosperm means covered seed.
3. 3The second difference follows from the first, and it concerns the structure of the seed and of the seedling. A gymnosperm seed is naked, contains no endosperm, and has a well-developed multicellular endosperm in the female gametophyte instead, and it has a variable number of cotyledons, from two in Pinus to many in Cycas. In an angiosperm the endosperm is formed by triple fusion and the cotyledons are fixed at two for a dicot and one for a monocot.
4. 4The third difference is the ultimate one and is worth stating as the reason the two are kept apart at all. In a gymnosperm the female gametophyte is retained within the ovule and the seed is naked; in an angiosperm the female gametophyte is reduced to just the few cells of the embryo sac and the megaspore is retained, so the angiosperm is more advanced in the reduction of the gametophyte.
5. 5The fourth difference is that the two reach dominance differently. Gymnosperms were dominant earlier in geological history and were the vascular plants of the coal age, whereas angiosperms became dominant later and are the dominant vascular plants today, so the two represent successive stages in the evolution of the seed habit.

Step-by-step solution

1. 1Heterospory is the production of two kinds of spores, microspores and megaspores, by the same plant, differing in size. The homosporous condition, in which one kind of spore is produced, is the general condition in the ferns and is called isosporous, and the two terms are opposites.
2. 2The two spores are formed in two different kinds of sporangia. The microspores are produced in a small microsporangium, are few in number, and are haploid; the megaspores are produced in a large megasporangium, are fewer and larger, and are also haploid. So heterospory is a condition in which the sporophyte produces dimorphic spores, and it is the precursor of the seed habit.
3. 3The significance is best given as a list of consequences, because that is how the question is marked. First, heterospory is a precursor of the seed habit, because the megaspore and the retained female gametophyte together anticipate the seed, and the retention of the megaspore within the megasporangium is the first step towards that.
4. 4Second, it is the forerunner of the embryo, because the retention of the megaspore and of the female gametophyte within the megasporangium, together with the formation of a protective jacket, is a step on the way to the embryo.
5. 5Third, and importantly, it alone makes the sexual reproduction of a seed plant possible, because only where the megaspore is retained on the parent sporophyte, as in heterosporous pteridophytes and in all seed plants, can the female gametophyte develop, be fertilised and be nourished on the parent before dispersal. Homosporous plants cannot retain the megaspore, because all their spores are alike and are dispersed together, so their female gametophyte grows outside the sporophyte. This is the single most important point to make.
6. 6The two examples to give are Selaginella and Salvinia, both heterosporous pteridophytes, and it is worth adding that all the seed plants, the gymnosperms and the angiosperms, are also heterosporous, which is why the condition is taken as such a significant step in evolution.

Step-by-step solution

1. 1(i) Protonema: the early, free-living, green, thread-like, haploid gametophytic stage in the life cycle of a moss, which develops on germination of a spore and later produces buds of leafy gametophores, which give rise to the plants. It is a characteristic stage of the moss life cycle and the example is Funaria, or Polytrichum.
2. 2(ii) Antheridium: the male sex organ, a multicellular, jacketed, club-shaped or cylindrical structure that produces the male gametes, the antherozoids or sperms, which are flagellated and motile. In bryophytes and pteridophytes it is borne on the gametophyte, and the example is the antheridium of Funaria, with the male gamete being a biflagellate antherozoid.
3. 3(iii) Archegonium: the female sex organ, a flask-shaped, multicellular, jacketed structure that produces a single egg. It has a swollen basal venter containing the egg and a neck with a venter canal, and it is the organ that makes a plant an archegoniate, or an Embryophyta. The example is the archegonium of a fern or of Marchantia, and its presence in the bryophytes, pteridophytes and gymnosperms is what unites the three groups as the archegoniates.
4. 4(iv) Diplontic: a type of life cycle in which the diploid sporophyte is the dominant and independent generation, the haploid gametophyte is small, reduced and dependent on the sporophyte, and the only haploid stage is the gamete itself. The example is a gymnosperm or an angiosperm, where the visible plant is 2n, and this is the life cycle of all seed plants.
5. 5(v) Sporophyll: a leaf-like structure in a sporophyte that bears sporangia, and in many plants it is specialised for reproduction rather than for photosynthesis. The examples to give are the sporophyll of a fern, which bears sporangia in sori, the microsporophyll or stamen and the megasporophyll or carpel of a flower, and the cone scale of Cycas.
6. 6(vi) Isogamy: a type of sexual reproduction in which the two gametes, the male and the female, are morphologically similar, of the same size and shape, so that they are indistinguishable, which is why the fusion is also called a/an amoeboid, or aplanogamous, type of fertilisation. The examples are the fusion of two similar flagellated gametes in Chlamydomonas and in Volvox, and the fusion of the two similar non-motile gametes in Spirogyra, Ulothrix and some species of Fucus.

Step-by-step solution

1. 1Write each as a paired set of contrasting points, and use the same headings in each half so the comparison is visible on the page.
2. 2(i) Red algae, the Rhodophyceae, differ from brown algae, the Phaeophyceae, in these ways. The pigment: red algae have chlorophyll a and d with red pigment r-phycoerythrin, while brown algae have chlorophyll a and c with the brown pigment fucoxanthin. The stored food: red algae store floridean starch, a carbohydrate closely related to glycogen and amylopectin, while brown algae store mannitol and laminarin, which are sugars. The flagella: red algae are generally non-motile and their cells have no flagella, while brown algae are motile and have two unequal flagella, one being tinsel and the other whiplash. The cell wall: the red algal wall has cellulose and galactans such as agar and carrageenan, while the brown algal wall has cellulose and algin, and it also contains alginates. Habitat: the red algae are mostly marine and are commonly found in deeper waters where less light penetrates, while the brown algae occur mostly in marine shallow and intertidal waters, with Fucus and Sargassum on the rocks between tides. Reproduction: the red algae have no motile reproductive bodies, their male gametes are non-motile and male and female gametes are not clearly distinguishable, whereas the brown algae have motile gametes, both male and female, and the male gametes are flagellated.
3. 3(ii) Liverworts, the Marchantiopsida or Hepaticae, differ from mosses, the Bryopsida or Musci, in these ways. The protonema: a liverwort has a short and small protonema, while a moss has a well-developed, long, branched and filamentous protonema. The sporophyte: the liverwort sporophyte is short, small and stalked, and the capsule contains spores with elaters, while the moss sporophyte is long, developed and differentiated into foot, seta and capsule, and the capsule contains spores with a peristome and does not contain elaters. The leaf arrangement: liverwort leaves are small and arranged in two rows, or are arranged spirally, while moss leaves are spirally arranged and are more like a miniature stem with a midrib. The thallus: the liverwort thallus is dorsiventral and ribbon-like, while the moss plant is radially symmetrical and erect. The gemma cup: the liverwort has gemma cups that help in vegetative reproduction, while the moss does not. Spore dispersal: the liverwort capsule bears hygroscopic elaters that twist with changes in humidity and help disperse the spores, while the moss capsule bears no elaters and instead has peristome teeth, which throw the spores out when the capsule dries.
4. 4(iii) A homosporous pteridophyte produces spores of one kind, and these are formed in one kind of sporangium; a heterosporous pteridophyte produces spores of two kinds, small microspores in a microsporangium and large megaspores in a megasporangium. Examples: the common fern such as Pteris is homosporous, whereas Selaginella and Salvinia are heterosporous. Significance: heterospory is a precursor of the seed habit, and it is significant because only in the heterosporous condition is the megaspore retained on the parent sporophyte, which is what allows the female gametophyte to be formed, fertilised and nourished on the parent, and this is the essential step towards the seed.

Step-by-step solution

1. 1The four matches are (a) to (iii), (b) to (iv), (c) to (ii) and (d) to (i), and the reasoning is simply the group each genus belongs to.
2. 2(a) Chlamydomonas is a unicellular, flagellated green alga, so it matches (iii) Algae.
3. 3(b) Cycas is a gymnosperm, the only living genus of the Cycadophyta, with naked seeds borne in a cone, so it matches (iv) Gymnosperm.
4. 4(c) Selaginella is a heterosporous pteridophyte, a heterosporous fern ally, so it matches (ii) Pteridophyte.
5. 5(d) Sphagnum is a moss, the peat moss that forms peat bogs, so it matches (i) Moss.

Step-by-step solution

1. 1Begin with the defining characters, the general life cycle, and then the four features the examination actually rewards: the seed, the vascular system, the reproductive structure and the life cycle.
2. 2The defining characters: the gymnosperms are the naked-seeded plants, the most highly evolved vascular plants without an obvious difference between the gametophyte and the sporophyte, and they dominate in the hills and temperate regions over vast areas of the world.
3. 3The plant body: the plant is a sporophyte, and it is differentiated into a root, a stem and leaves. The root is a tap root, the stem is well developed, and the leaves are small, thick, needle-like with a thick cuticle, sunken stomata and a single unbranched vein, so the leaves are adapted to reduce water loss. The vascular system is well developed, and the xylem lacks vessels and has only tracheids, which is a diagnostic feature to remember. The gymnosperms are heterosporous.
4. 4The seed is naked and borne on the megasporophyll, and the seed is large and winged or fleshy, with a seed coat. Crucially the seed contains no endosperm, because the nourishment is stored in the multicellular female gametophyte, and the number of cotyledons varies from two to many, which is a further diagnostic point.
5. 5The reproductive structures: the male and female cones or strobili are the reproductive organs, so a gymnosperm is described as a heterosporous plant with male and female cones. The male cone has microsporophylls bearing microsporangia, and the pollen is released and carried by the wind, so pollination is by wind and the plant is monoecious with a sporophytic and dominant life cycle, and the female cone has megasporophylls bearing ovules. There is no true fruit, because there is no ovary, and that is the character that separates the group from the angiosperms.